253 FXUS64 KFWD 080433 AFDFWD Area Forecast Discussion National Weather Service Fort Worth TX 1033 PM CST Thu Feb 7 2019 .UPDATE... /Rest of Tonight/ No major changes are needed to tonight's forecast. Cold and breezy conditions will persist as lows are expected to drop into the 20s across North and Central Texas. Northerly winds will yield wind chill values in the teens by sunrise. Cirrus clouds will continue to stream across Central Texas through the night. Low level clouds will creep northward from the Hill Country around sunrise as additional moisture returns to the region. Hernandez && .AVIATION... /Issued 623 PM CST Thu Feb 7 2019/ /00Z TAFs/ Post-frontal low clouds have moved off to the south and east of the region as drier air makes its way from the north. Breezy northerly winds will continue through the remainder of the night before a gradual veering begins Friday afternoon. Although VFR is expected through 00Z Saturday, ceilings will begin a slow decreasing trend beginning mid-day Friday as moisture makes a return to the area. Upper level southwesterly flow will keep a consistent stream of cirrus through the remainder of this cycle. Although the extended portion of the KDFW forecast remains dry, we will continue to monitor the possibility of frozen precipitation in the afternoon and evening. Confidence in frozen precipitation coverage remains low, therefore, will hold off on adding it at this point. Hernandez && .SHORT TERM... /Issued 401 PM CST Thu Feb 7 2019/ /Through Tonight/ Unseasonably rich boundary layer moisture contributed to the intensity of the thunderstorms accompanying the early morning frontal passage. Once lifted by the advancing boundary, this moisture became the postfrontal cloud bank that has been difficult to erode. Guidance tends to struggle with anomalies of this sort, but the extent of today's cloud cover was only one of the shortcomings. Model output often downplays the intensity of cold advection within an arctic air mass, and today was a stark example, the warm bias further accentuated by the underestimated cloud cover. As a result, our forecast temperatures through the evening hours are a handful of degrees below guidance. With additional dry advection, a deepening postfrontal boundary layer is steadily losing its low clouds. Sun filtering through an icy cirrostratus veil has allowed afternoon temperatures to warm a few degrees after their midday minimums. But with the falling sun angle, the cold advection will soon win out, and temperatures will rapidly fall this evening. The high clouds will do little to stem the temperature drop, and although dew points will plunge into the teens and even single digits, the diminishing but steady north winds will prevent Friday morning's low from reaching their full radiational cooling potential. Nevertheless, daybreak readings will be around 10 degrees below early February normals, ranging from near 20F in the north and northwest to around freezing along our southeastern boundary. 25 && .LONG TERM... /Issued 401 PM CST Thu Feb 7 2019/ /Friday and Beyond/ The primary concerns in the long-term portion of the forecast will be the potential for wintry precipitation on Friday and Friday night, and widespread rainfall Saturday night through Monday morning. A potent shortwave trough, presently off the Baja Coast, will move quickly along the International Border and into West Texas by late Friday. Increasing large-scale ascent in the form of an upper-level potential vorticity anomaly will lead to increasing cloud cover from southwest to northeast across Central and North Texas. While the sub-cloud layer will be dry initially, profiles will moisten throughout the day as isentropic ascent transports Pacific moisture into the region. These moistening profiles concurrent with aforementioned synoptic-scale ascent will lead to the development of patchy areas of light precipitation by Friday afternoon, initially over the Hill Country, and spreading northeast into the evening hours. One of the bigger challenges with Friday's forecast was high temperatures. Model guidance has struggled with today's (Thursday's) temperatures behind the strong arctic cold front that passed this morning, with most guidance being some 5-10 degrees too warm. Following morning lows in the 20s across most of the county warning area (CWA) Friday morning, temperatures will likely only climb into the upper 30s (perhaps the very low 40s) for most areas as modest cold air advection continues in the form of northeast winds at around 10 knots. Increasing cloud cover will also limit the amount of heating from insolation, though this cloud cover will likely arrive later in the day for areas north of Interstate 20. Should cloud cover move farther north faster than anticipated, the forecast highs for Friday could be too high (the official forecast lows are already a little below guidance). The precipitation type forecast for Friday is also tricky. NAM forecast soundings reveal that in the morning, high cloud bases at around 16,000 feet will be present above a deep and dry sub- cloud layer. This will result in most hydrometeors evaporating or sublimating before reaching the ground. As profiles moisten late in the day however, precipitation should be able to reach the ground. Two precipitation regimes are expected to be present across our CWA. (1) Over roughly the northern half of our CWA (including the Dallas/Fort Worth Metropolitan Area), profiles should be saturated from about 2,000 feet AGL to above the dendritic growth zone (the layer where temperatures are in the range of -10 C to -20 C, wherein conditions are most favorable for ice crystal formation). This means any precipitation would fall as snow. A slight warm nose is forecast to exist at around 800 mb, so some sleet pellets may occur as well. (2) Over the southern half of our CWA (including Waco, Killeen, Temple, and Palestine), a saturated dendritic growth zone should be present, but a significant warm nose should develop and sharpen with time at around 700 mb. This means any frozen precipitation in this region would reach the ground as sleet. In terms of amounts, the limited amount of moisture and modest upper-level support should keep the precipitation rates very light. Furthermore, a recent warm spell has allowed ground temperatures to warm substantially, and with temperatures forecast to be above freezing for much of the day Friday, little to no accumulation is expected. That being said, the potential will exist for short "bursts" of moderate sleet and/or snow, which could lead to localized light accumulations and reductions in visibility, which would lead to minor travel impacts. The greatest probability of experiencing one of these bursts likely exists roughly within a corridor from Hillsboro to Athens to Tyler, including some of the very southern fringes of the Dallas/Fort Worth area. The best timing would be during the evening and overnight hours Friday. It should be stressed however that pinpointing the exact location of a heavier band of wintry precipitation is extremely challenging. Most locations will likely not see any accumulating wintry precipitation at all, but it is always safe to be prepared just in case, since the chance for accumulation, while low, does exist. Precipitation should come to a brief end Saturday morning as the upper-level potential vorticity anomaly moves off to the east. Another upper-level disturbance will move into the area Saturday evening however, setting off another round of precipitation. Temperatures should be warmer however, and wintry precipitation is not expected with this event. The main focus for rainfall on Sunday will be a warm front (actually a retreating cold front) which will move northeast to near our southeastern and eastern CWA boundary. Rainfall rates will not be particularly heavy, but a steady rain is expected for most of the day, which will bring event total QPF to around half an inch for most areas along and east of Interstate 35, with a few spots in our northeastern counties potentially seeing over one inch. The low rain rates should minimize the threat for flooding. With regards to temperatures on Sunday, forecast highs are well below guidance, which has been trending colder (but remains well above freezing), and to account for the widespread cloud cover and precipitation. Rain chances should end by Monday afternoon and evening for most locations. Towards the middle of next week, temperatures should moderate to near seasonal normals as zonal flow (to slight ridging) sets up across the southern CONUS. Godwin && .PRELIMINARY POINT TEMPS/POPS... Dallas-Ft. Worth 25 39 32 43 38 / 0 10 30 10 60 Waco 27 39 35 42 38 / 0 20 50 20 50 Paris 22 40 31 43 36 / 0 10 20 5 60 Denton 23 39 30 43 36 / 0 10 20 5 50 McKinney 22 40 31 42 37 / 0 10 20 5 60 Dallas 25 40 33 43 38 / 0 10 30 10 60 Terrell 24 39 33 43 37 / 0 10 40 5 60 Corsicana 25 41 34 41 38 / 0 20 50 10 50 Temple 26 39 35 42 39 / 0 40 50 30 50 Mineral Wells 22 38 30 41 35 / 0 10 20 10 40 && .FWD WATCHES/WARNINGS/ADVISORIES... None. && $$ 08